This invention relates to a method for splicing optical fibers with each other, more particularly, a method for joining together optical fibers having a core coated with a plastic clad layer, by fusing the core, and to an optical fiber suited for carrying out the method.
Among various types of optical fibers, there are ones having a clad layer made of a plastic material. This type of optical fibers has a structure such that a plastic clad layer, a cushioning layer, and a protective layer are coated in sequence around the core. To join optical fibers of this type with each other, an optical connector is used to detachably connect the fibers, or the cores of the fibers are directly spliced with each other.
The method using an optical connector, however, has the problem that peeling of the connecting portions of optical fibers occurs due to a difference in the coefficient of thermal expansion between the core and the above-mentioned layers, as is evidenced by a heat cycle test carried out with a temperature range of -20.degree. C. to 60.degree. C., for example. Accordingly, when high reliability of connection between optical fibers and miniaturization of the connecting potion are required, for example, when optical fibers arranged outdoors need to be connected to ones arranged indoors, a method of joining optical fibers by fusing the cores, namely, a fusion bonding method, is employed.
According to the fusion bonding method, to expose the core of an optical fiber, the protective layer, the cushioning layer and the clad layer must be removed, but since the clad layer, in particular, firmly adheres to the core, every caution must be taken when removing the clad layer. When a hand tool such as a knife is used to remove the clad layer, the surface of the core may be damaged by chance, causing a problem in that the splice loss is increased and the strength is decreased at the connected portion. Therefore, instead of using a hand tool to remove the clad layer, other methods are employed, considering that the clad layer is made of a plastic material, in general, a silicone resin; for example, a method of dissolving the clad layer in a solvent, a method of causing an organic solvent, such as benzene, or a strong acid, such as concentrated sulfuric acid, to penetrate through the clad layer to swell the same and removing the swollen clad layer, and a method of removing the clad layer after the layer is deteriorated by heat. These methods of removing the clad layer without the use of a hand tool, however, have the following disadvantages. Namely, for optical fibers which have already been installed, there is no solvent suited for removing the clad layer of the laid optical fibers. Therefore, the connecting operation cannot be carried out safely and easily and the disposal of the used solvent calls for the greatest care in view of environmental preservation. In the case of deteriorating the clad layer by heat, the clad layer is heated by a gas burner, for example, but this operation involves danger and the core itself can be made very brittle due to heat.